A technique of preparing a poly(meth)acrylate ester by using a chain transfer agent in radical polymerization is known conventionally. In this polymerization technique, however, the terminal structure of the polymer is generally not fixed owing to the termination of disproportionation or chain transfer into the solvent, monomer or initiator employed, which makes it difficult to control the terminal structure of the polymer. This also becomes a cause for the deterioration of the thermal decomposition resistance of the polymer.
In addition, known is a technique of controlling the polymerization of a (meth)acrylate ester by using a chain transfer agent in living polymerization (Japanese Patent Application Laid-Open No. 133212/1986). In this polymerization technique, a tetracoordinate organosilicon, organotin or organogermanium compound is used as a polymerization initiator and in addition, a co-catalyst system which is a ion source, such as bifluoride, fluoride, cyanide or azide; or a suitable oxyanion, a Lewis acid or a non-anionic Lewis base is employed. Although the molecular weight of the polymer prepared by this polymerization technique can be controlled, it has not sufficient steric regularity.
On the other hand, as a technique of preparing a poly(meth)acrylate ester by using an organometallic compound, particularly, an organic rare earth metal compound, conventionally known are a preparation process (Japanese Patent Application Laid-Open No. 258808/1990) of a vinyl polymer by using a divalent rare earth metal compound and a preparation process (Japanese Patent Application Laid-Open No. 263412/1991) of a poly(meth)acrylate ester by using a trivalent rare earth metal compound. These polymerization techniques make it possible to prepare a syndiotactic poly(meth)-acrylate ester having narrow molecular weight distribution and a high molecular weight.
The above-described polymerization system formed with the divalent rare earth metal compound or trivalent rare earth metal compound as a polymerization initiator is accompanied with the drawbacks such that 1) the molecular weight of the polymer can be controlled only by a monomer/initiator ratio, 2) the organometallic compound used as an initiator remains in the resulting polymer and colors the polymer, 3) use of an expensive initiator in a large amount is required, and 4) the resulting polymer has low thermal decomposition resistance.